Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$83.94	8.284%	$90.8936	$90.89	$90.90	$90.90
Purchase #2	$107.73	5.364%	$113.5086	$113.51	$113.50	$113.50
Purchase #3	$47.82	13.825%	$54.4311	$54.43	$54.45	$54.40
Purchase #4	$42.64	9.854%	$46.8417	$46.84	$46.85	$46.80
Purchase #5	$7.66	8.387%	$8.3024	$8.30	$8.30	$8.30
Purchase #6	$52.52	3.376%	$54.2931	$54.29	$54.30	$54.30
Purchase #7	$136.72	8.610%	$148.4916	$148.49	$148.50	$148.50
7 purchase totals =	$479.03		$516.7621	$516.75	$516.80	$516.70